The rates of synthesis of the polyamines (spermidine and spermine) and their metabolic precursor putrescine are elevated during the proliferative response of mammalian cells. The cellular levels of two key enzymes of polyamine biosynthesis, ornithine decarboxylase, and S-adenosylmethionine decarboxylase, are greatly elevated early in the response of small lymphocytes to mitogenic activation. Initially, the studies have concentrated on regulation of S-adenosylmethionine decarboxylase. The enzyme has been purified and rabbit antiserum and mouse monoclonal antibodies have been prepared to it. We have measured the rate of synthesis in intact lymphocytes and it is stimulated 10-fold within 9 hrs after mitogenic activation. cDNA clones coding for S-adenosyl-methionine decarboxylase have been prepared using synthetic DNA probes, based on amino acid sequences from the protein to screen a bovine lymphocyte cDNA library. These recombinant DNA probes are being used to investigate the mechanism of translational and transcriptional control of this enzyme in mitogen-activated lymphocytes. (J)